Antennas in hand-held devices such as mobile phones or receivers for satellite navigation systems represent the interface between the hand-held device and the wireless transmission channel, over which electromagnetic signals of a given bandwidth and center frequency are received and/or transmitted. The gain of an antenna for a given frequency range thus is generally considered as an important factor in link budget considerations that determine the maximum transmission power and its dynamic range for both the hand-held device and the device the hand-held device is transmitting to or receiving from. With hand-held devices being battery-powered, it is highly desirable to reduce the required transmission powers to increase the operating time of the hand-held device. Inter alia, this can be achieved by increasing the antenna gain.
The gain of an antenna is generally both frequency- and angle-dependent, and consequently, it is the primary aim of antenna design to achieve satisfactory gain behaviour for a given frequency range and angular domain. Secondary aims that become more and more important with the increasing miniaturisation of hand-held devices and the growing competition are small antenna sizes, less weight and reduced costs. With the advent of hand-held devices that are capable of operating different mobile radio system standards (e.g. the Global System for Mobile Communications (GSM) or the Universal Mobile Telecommunications System (UMTS)) and further radio system standards such as satellite navigation system standards (e.g. the Global Positioning System (GPS) or the Galileo system) or short-range wireless communication standards (e.g. the Bluetooth short-range device interconnection system), antenna design further faces the requirement to cover several frequency ranges with one antenna structure or to efficiently combine antennas for each required frequency range into one device. The portability of antenna designs from one hand-held device to a second hand-held device, which is highly desirable to reduce R&D costs, in particular is aggravated by the effect that the antenna characteristics are heavily influenced by other metallic parts of the hand-held device, for instance the central circuit board of the hand-held device. However, for some antenna types, these other metallic parts of the hand-held device are intentionally used as a surrogate for a ground plane, so that lack of portability is inherent to the antenna design.
FIG. 1 depicts an example of a state-of-the-art antenna structure of a mobile-phone in exploded view. The antenna structure consists of an antenna carrier 1, a flex-print structure 2, pogo pins 3-3 . . . 3-7 and a decorative label 4, which are all assembled as indicated by the exploded view.
The antenna carrier 1 consists of a crystalline polymer (Questra) and, except for the reinforced parts, has a thickness of 800 μm. It should be noted that this value, similar as all other exact values provided in this description, is to be taken as an exemplary value which does not restrict the scope of the invention.
The flex-print 2 is a one-layer Printed Wiring Board (PWB) consisting of a 100 μm layer of Polyethylene Terephthalate (PET), a 20 μm copper layer that covers the PET layer and an 100 μm adhesive layer below the PET layer. In FIG. 1, the flex-print 2 is seen from the backside, so that the adhesive layer is facing the antenna carrier 1.
By punching out or etching, two radiation structures 2-1 and 2-2 have been formed on said flex-print 2, i.e. copper from said flex-print 2 has been removed so that only the copper that forms the radiation structures 2-1 and 2-2 is left on the PET layer. Said radiation structures 2-1 and 2-2 formed of copper on said PET layer face the decorative label 4 and are thus depicted in dashed lines. Radiation structure 2-1 represents a Planar-Inverted-F-Antenna (PIFA) suited for use in the frequency range of mobile radio systems such as for instance the GSM or UMTS. Note that, for the PIFA, both the radiation structure 2-1 and the ground plane are formed in copper on the PET layer of flex-print 2, thus the dashed lines depicted in FIG. 1 illustrate both the radiation structure 2-1 and the ground plane of said PIFA. Radiation structure 2-2 represents a line-shaped, partially bent antenna that is suited for use in the frequency range of the Global Positioning System (GPS).
The flex-print 2 further comprises noses 2-3 . . . 2-7 that are fabricated by partially cutting the copper-clad portions on said flex-print 2 and bending the respective part of the flex-print between the cuts so that respective noses 2-3 . . . 2-7 arise that are rectangular to the flex-print 2. The noses 2-3 . . . 2-7 allow to electrically contact the radiation structures 2-1 and 2-2, and, in the case of the PIFA, also the ground plane of the PIFA that is also formed in copper on the PET layer of flex-print 2. When said flex-print 2 is attached to said antenna carrier 1, the noses 2-3 . . . 2-7 penetrate the respective openings 1-3 . . . 1-7 formed in the antenna carrier. If then metallic pogo pins 3-3 . . . 3-7 are snapped into these respective openings 1-3 . . . 1-7, the noses 2-3 . . . 2-7 are crimp-connected to said respective pogo pins 3-3 . . . 3-7. The radiation structure 2-2 (pogo pin 3-6 and/or 3-7) and 2-1 (pogo pin 3-3) and the ground plane (pogo pins 3-4 and 3-5) of the PIFA antenna can then be contacted via the top of the respective pogo pin 3-3 . . . 3-7 that protrudes through the respective opening 1-3 . . . 1-7.
The final application of the decorative label 4, in the example of FIG. 1 a 200 μm thick layer, protects the flex-print 2 and in particular the radiation structures 2-1 and 2-2 from physical damage and corrosion.
Due to the fact that two antennas are integrated into the antenna structure of FIG. 1, namely one GPS antenna and one antenna for a mobile radio system, the exploitable degrees of freedom in antenna design are limited, in particular with respect to the available area that can be used for the layout of the antennas.